Are there such things as "root objects"?
If you want to make an object the parent of several objects, select the objects, then, at last, the parent, and press ctrlP (Set Parent To) > Object. You can also create an empty, shiftA (Add) > Empty > Plain Axes, and make it the parent of your object with the same Set Parent To operation. To deparent, select the object and altP > Clear Parent. You can know what's the parent of an object if you select it, go in the Properties panel > Object > Relations > Parent.

Does it answer?